[Interpreter] Preserve source positions in peephole optimizer.

test/cctest/interpreter/bytecode_expectations/UnaryOperators.golden

 #
 # Autogenerated by generate-bytecode-expectations.
 #
 
 ---
 pool type: number
 execute: yes
 wrap: yes
 
 ---
@@ skipping 88 matching lines @@
 ]
 
 ---
 snippet: "
   var x = 1234;
   var y = void (x * x - 1);
   return y;
 "
 frame size: 4
 parameter count: 1
-bytecode array length: 23
+bytecode array length: 24
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /*   42 S> */ B(Wide), B(LdaSmi), U16(1234),
   /*   42 E> */ B(Star), R(0),
   /*   56 S> */ B(Star), R(2),
   /*   66 E> */ B(Ldar), R(0),
                 B(Mul), R(2),
                 B(Star), R(3),
                 B(LdaSmi), U8(1),
                 B(Sub), R(3),
                 B(LdaUndefined),
   /*   56 E> */ B(Star), R(1),
+  /*   74 S> */ B(Nop),
   /*   84 S> */ B(Return),
 ]
 constant pool: [
 ]
 handlers: [
 ]
 
 ---
 snippet: "
   var x = 13;
@@ skipping 53 matching lines @@
   /*   46 S> */ B(Star), R(1),
                 B(LdaSmi), U8(-1),
                 B(Mul), R(1),
   /*   57 S> */ B(Return),
 ]
 constant pool: [
 ]
 handlers: [
 ]